import java.util.Scanner;

//递归求斐波那契数列的第 N 项
public class TextDemo {
    public static int fib(int n){
        if(n==1||n==2){
            return 1;
        }
        else {
            return fib(n-1)+fib(n-2);
        }

    }
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int ret=fib(n);
        System.out.println(ret);


    }
}
